1. Field of the Invention
This invention relates to a semiconductor device and a semiconductor integrated circuit and, more particularly, to a semiconductor device and a semiconductor integrated circuit comprising an electrically programmable fuse element.
2. Description of the Related Art
Some methods are known to implement a memory circuit capable of storing data with nonvolatility in a semiconductor device. For example, when a large storage capacity is needed and rewriting data at a number of times is required, a flash memory comprising a memory cell of a stacked gate structure is used. In this case, an especial process different from a standard CMOS process is needed. In a memory circuit such as a memory LSI whose main purpose is to store data with nonvolatility, overhead costs for use of the dedicated process can be reduced by increasing the storage capacity.
In a system LSI or the like, however, overhead costs are increased by using a dedicated process only to store small capacity data such as security data, code data, ID data inherent to a chip, trimming data and the like with nonvolatility. In addition, rewriting data at as many as one hundred thousand times as conducted on a flash memory is not needed though it depends on its purpose. If semi-fixed data is stored with nonvolatility and may be rewritten as occasion requires, rewriting is conducted at a few times. Use of a flash process which requires high costs to be paid for guarantee of rewriting data at as many as one hundred thousand times, for such a purpose, is not advantageous. In this case, it is therefore preferable to use a nonvolatile memory element which can be formed in a standard CMOS process.
A fuse element is widely known as the nonvolatile memory element which can be implemented in a standard CMOS process. In general, a fuse element (o-fuse, optical-fuse) programmed by a laser beam or a fuse element (e-fuse, electrical-fuse) as electrically programmed is used as the fuse element. As the o-fuse, metal or polysilicon wiring is used as the fuse element and data is programmed by applying a laser beam to the fuse element and blowing the fuse element.
On the other hand, as for the e-fuse, for example, an oxide film which is an insulator is used as the fuse element, and data is programmed by breaking the oxide film by application of a high voltage stress and making the oxide film conducting. In other words, data is stored by making the oxide film conducting/nonconducting. As for the other e-fuse, polysilicon wiring having a salicide layer formed on a surface thereof by a salicide process is used as a fuse element, the salicide layer is broken and a resistance value is increased by making current flow by application of high voltage, and data is stored in accordance with variation in the resistance value.
In the e-fuse, an especial apparatus or process is not required for blow. For this reason, the e-fuse can be programmed even after packaging or integration into a system, though the o-fuse needs to be programmed in a state of wafer.
Therefore, the e-fuse becomes used in a wider range, not only for the purpose of storing redundancy data used in a redundancy circuit which rescues a defective memory cell, code data, ID data inherent to the chip, trimming data used to adjust the timing or voltage, and the like, as a substitute to the o-fuse, but also for the purpose of storing encryption data or data stored in an external nonvolatile memory to a chip.
In accordance with such an increasing range of uses, the number of fuse elements (e-fuse) mounted on the LSI is increased. In accordance with this, there is higher possibility that defective fuse elements (e-fuse) which cannot be programmed with normal data are included in the mounted fuse elements (e-fuse), due to defect in process. If even one defective e-fuse exists, a macroblock comprising the e-fuse cannot be used and the LSI chip comprising the macroblock becomes a defective item.
As a related technique of this kind, a technique of replacing defective fuses to conduct redundant rescue is disclosed (see Jpn. Pat. Appln. KOKAI Publication No. 2001-35185).